13. The transition from mediaeval housekeeping, with its use values and private exchange, to the mercantile society of modern times, was not made in a day, nor went on everywhere at the same rate. It was a growth of ages. In great cities commerce rapidly ripened, and was well on towards maturity five centuries ago. Then the conditions that render interest lawful, and mark it off from usury, readily came to obtain. But those centres were isolated. Like the centres of ossification, which appear here and there in cartilage when it is being converted into bone, they were separated one from another by large tracts remaining in the primitive condition. Here you might have a great city, Hamburg or Genoa, an early type of commercial enterprise, and, fifty miles inland, society was in its infancy, and the great city was as part of another world. Hence the same transaction, as described by the letter of the law, might mean lawful interest in the city, and usury out in the country--the two were so disconnected. In such a situation the legislator has to choose between forbidding interest here and allowing usury there; between restraining speculation and licensing oppression. The mediaeval legislator chose the former alternative. Church and State together enacted a number of laws to restrain the taking of interest, laws that, like the clothes of infancy, are not to be scorned as absurd restrictions, merely because they are inapplicable now, and would not fit the modern growth of nations. At this day the State has repealed those laws, and the Church has officially signified that she no longer insists on them. Still she maintains dogmatically that there is such a sin as usury, and what it is, as defined in the Fifth Council of Lateran. _Readings_.--St. Thos., 2a 2æ, q. 77, art. 1; Ar., _Pol_., I., ix.; St. Thos., 2a 2æ, q. 77, art. 4; _The Month_ for September, 1886; _The Nineteenth Century _for September, 1877, pp. 181, seq. CHAPTER VI. OF MARRIAGE. SECTION I.--_Of the Institution of Marriage_. 1. Marriage is defined by the Canonists: _the union of male and female, involving their living together in undivided intercourse_. In the present order of Providence, the marriage contract between baptized persons is a sacrament, under the superintendence of the Church, the fertile theme of canonists and theologians. As philosophers, we deal with marriage as it would be, were there no sacraments, no Church, and no Incarnation, present or to come. This is marriage in the order of pure nature.